This application claims the priority benefit of Taiwan application serial no. 88113558, filed Aug. 9, 1999, the full disclosure of which is incorporated herein by reference.
1. Field of Invention
The present invention relates to a type of anti-counterfeiting tag. More particularly, the present invention relates to the structure of a diffractive anti-counterfeiting tag with capabilities of naked-eye inspection and machine inspection and its method of manufacture.
2. Description of Related Art
A hologram is a diffractive component that is frequently used as a means of authenticating products, improving security and preventing unlawful copying activities. For example, the dove on a VISA card and the globe on a Master card are holograms. The hologram on the VISA or Master card is able to prevent counterfeiting activities because it is difficult to copy the image just by scanning or printing. Only professional people who are familiar with holographic techniques can reproduce a hologram.
Nevertheless, a hologram can still be reproduced by copying, although the image copied from an original hologram is likely to have an inferior quality plus other defects. However, to distinguish a genuine hologram from a faked one by naked-eye inspection, specially trained people must be employed. Moreover, people""s judgements are often clouded by subjective factors.
In addition to human-eye inspection of hologram, specially hidden patterns can also be added alongside the visible hologram. For example, according to U.S. Pat. No. 4,984,824, an anti-counterfeiting tag having both a visible hologram and a diffractive hidden pattern is proposed. This type of anti-counterfeiting tag must be inspected with a magnifying glass. Aside from the few people who are familiar with the product, very few people are able to pick up the hidden pattern. Moreover, dimensions and details within the area holding the hidden pattern are more precisely manufactured, thereby increasing the level of difficulty for counterfeiting. However, the hidden pattern can still be discerned by careful observation and then faked, and the hidden pattern is similarly assessed by subjective inspectors.
Machine inspection, by comparison, is a more objective method of distinguishing a genuine from a faked pattern. However, due to the necessity of alignment between the machine and the pattern, the aforementioned diffractive hidden pattern is not particularly suitable for machine inspection. To facilitate tag inspection using a machine, a system combining a bar code and a hologram is proposed in U.S. Pat. Nos. 5,306,899 and 5,422,744. The combination of a bar code and a hologram is able not only to increase the level of security for counterfeiting, but objective machine measurement is also possible. Nonetheless, the bar code can be read out by any bar code reader, and so the bar code can be easily reproduced.
In general, a diffractive component is difficult to counterfeit and is also suitable for machine inspection. Hence, diffractive components are very often used on anti-counterfeiting tags in anti-counterfeiting systems. First, a suitable diffractive pattern is designed according to need. Second, a suitable detector is mounted in a position for reading the anti-counterfeiting tag. Third, an analyzing machine is used to judge the genuineness of the tag according to the feedback signals from the detector. Because the analyzing machine for judging the tag is part of the anti-counterfeiting system, the integration of the analyzing machine and the diffractive component increases design flexibility and level of counterfeiting prevention. In addition, efficiency of any copied diffractive components is likely to be lower than the original, and hence can be quite easily singled out by the analyzing machine.
In general, a diffractive anti-counterfeiting tag will produce a collection of lighting spots. For example, according to U.S. Pat. Nos. 5,291,006, 5,300,764 and 5,627,663, the diffractive component of the anti-counterfeiting tag is subdivided into a plurality of blocks. Each of these blocks has a linear diffraction grating that has a different orientation and/or line width. A laser diode or a photodiode is used to illuminate the grating so that a detector array or a diffracted pattern is formed for machine analysis. For example, in the Microtag system as described in Opt. Lett., Jan. 1, 1998, an extreme ultraviolet (EUV) lithographic method is used so that a plurality of blocks of linear diffraction gratings each having a specific line width and phase difference are formed. The analyzing machine comprises a laser diode and a charge-coupled device (CCD). However, the basic unit of the anti-counterfeiting tag is a linear diffraction grating. FIG. 1 is a schematic, top view showing a plurality of the linear diffraction gratings in a conventional anti-counterfeiting tag. Therefore, any would-be counterfeiter can still mark down such information as the orientation, cycle and line width in each diffraction grating block and reproduce the pattern accordingly.
The present invention provides a diffractive anti-counterfeiting tag structure and a method of fabricating the tag. The diffractive anti-counterfeiting tag comprises a hologram for naked-eye inspection and a non-grating diffractive component for machine inspection. Hence, the tag has double protection against any unlawful copying and counterfeiting.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a diffractive anti-counterfeiting tag structure. The tag includes a hologram and a non-grating diffractive component that are bonded together by a board-joining technique or a random pixel design. Consequently, the hologram and the non-grating diffractive component are integrated together to form a diffractive anti-counterfeiting tag. The hologram permits naked-eye inspection for picking out the counterfeits, while the non-grating diffractive component is able to produce an irregular image permitting an anti-counterfeiting machine to decide upon the question of genuineness. Therefore, the diffractive anti-counterfeiting tag of this invention is doubly protected against copying or counterfeiting.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.